Implant magnet system

ABSTRACT

A magnetic alignment system that can form part of a cochlear implant system. The magnetic alignment system prevents substantial movement of a magnet of an implanted component during an MRI procedure or allows for easy removal of the magnet to facilitate the MRI procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 11/857,397 filed Sep. 18, 2007, now U.S. Pat. No.8,255,058 issued Aug. 28, 2012, which claims priority from U.S. patentapplication Ser. No. 10/820,444, filed on Apr. 8, 2004, which claimspriority from Australian Provisional Application No 2003901696, filedApr. 9, 2003, the contents of which are incorporated herein byreference.

BACKGROUND Field of the Invention

The present invention relates to a cochlear implant and in particular toan MRI-compatible implantable component of a cochlear implant.

Cochlear implant systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.

Typically, cochlear implant systems have consisted of essentially twocomponents, an external component commonly referred to as a processorunit and an internal implanted component commonly referred to as astimulator/receiver unit. Traditionally, both of these components havecooperated together to provide the sound sensation to a user.

The external component may consist of a microphone for detecting sounds,a speech processor that converts the detected sounds, particularlyspeech, into a coded signal, a power source such as a battery, and anexternal transmitter antenna.

The coded signal output by the speech processor is transmittedtranscutaneously to the implanted stimulator/receiver unit that can besituated within a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs via the external transmitter antennawhich is positioned to communicate with an implanted receiver antennaprovided with the stimulator/receiver unit.

The implanted stimulator/receiver unit traditionally includes a receiverantenna that receives the coded signal and power from the externalprocessor component, and a stimulator that processes the coded signaland outputs a stimulation signal to an intracochlear electrode assemblywhich applies the electrical stimulation directly to the auditory nerveproducing a hearing sensation corresponding to the original detectedsound.

The commonly accepted method of providing the implanted stimulator withpower and information is to transmit RF-power via an inductively coupledantenna coil system. In such a system, the external transmitter coil isusually positioned on the side of an implantee's head directly facingthe implanted coil of the stimulator/receiver unit to allow for thetransmission of the coded sound signal and power from the speechprocessor to the implanted unit. Such transmitters usually have a coilformed by a small number of turns of a single or multi-strand wire and amagnet at or near the hub of the coil. The magnet holds the transmittercoil in place due to magnetic attraction with a magnet of the implantedunit.

The implanted magnet can pose problems for those cochlear implantimplantees that may be required to undergo magnetic resonance imaging(MRI). In this regard, although studies have indicated that MRI presentsno major risk to such implantees, the magnetic fields used in MRIprocedures have been shown to exert a torque force on the implantedmagnet. This torque force, if significantly large, such as may be thecase if a high field strength MRI is undertaken, has the potential tocause undesirable consequences such as dislodgement of the magnet fromits casing as well as discomfort to the implantee. There is also thepotential for significant distortion of the image obtained by MRI due tothe presence of the magnet in the implantee's head, which maysignificantly negate the usefulness of the process.

SUMMARY

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

In a first aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0012] the system beingcharacterised in that an outer surface of the magnet, or a casing forthe magnet, of the implantable receiver component has an engagementsurface that is engageable with a complementary engagement surfaceformed in a mounting of the implantable receiver component.

In a second aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0014] the system beingcharacterised in that the magnet of the implantable receiver componentis housable within a pocket formed in a suitable biocompatible flexiblemounting, said pocket having a restricted opening formed therein throughwhich the magnet is insertable but which is sized to retain the magnetwithin the pocket following insertion.

In a third aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0016] the system beingcharacterised in that the magnet of the implantable receiver componentis housed within a suitable biocompatible flexible mounting, saidmounting having one or more indicia thereon or therein that identify thelocation of the magnet within the mounting

In a fourth aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0018] the system beingcharacterised in that the magnet is releasably held within the receivercomponent by one or more retaining devices.

In a fifth aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0020] the system beingcharacterised in that the magnet of the implantable receiver componentis housed within a recess formed in a suitable biocompatible flexiblemounting, said recess being locatable adjacent the skull of theimplantee in use thereby ensuring the magnet is held in the recessbetween the receiver component and the skull of the implantee

In a sixth aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, the external transmitter unit having a magnetpositioned therein and the implantable receiver component having amagnetised insert positioned therein to allow transcutaneous alignmentof said external transmitter unit and said implantable receivercomponent; [0022] the magnetised insert of the implantable receivercomponent having a first end and a second end and increasing in widthaway from said first end towards said second end, the first end beingpositionable closer to the skin of the implantee in use to ensureself-centering of the magnet of the external transmitter unit with themagnetised insert of the receiver component

In a seventh aspect, there is provided a magnetic alignment system for atranscutaneous transmitter/receiver system, said magnetic alignmentsystem comprising an external transmitter unit and an implantablereceiver component, both the external transmitter unit and theimplantable receiver component having a magnet positioned therein toallow transcutaneous alignment of said external transmitter unit andsaid implantable receiver component; [0024] the system beingcharacterised in that the implantable receiver component is detachablyconnectable to an implantable tissue stimulator device.

In an eighth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component; wherein an outer surface of themagnet, or a casing for the magnet, of the implantable receivercomponent has an engagement surface that is engageable with acomplementary engagement surface formed in a mounting of the implantablereceiver component.

In a ninth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component and wherein the magnet of theimplantable receiver component is housable within a pocket formed in asuitable biocompatible flexible mounting, said pocket having arestricted opening formed therein through which the magnet is insertablebut which is sized to retain the magnet within the pocket followinginsertion.

In a tenth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component; wherein the magnet of theimplantable receiver component is housed within a suitable biocompatibleflexible mounting, said mounting having one or more indicia thereon ortherein that identify the location of the magnet within the mounting

In an eleventh aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component; wherein the magnet isreleasably held within the receiver component by one or more retainingdevices.

In a twelfth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component; wherein the magnet of theimplantable receiver component is housed within a recess formed in asuitable biocompatible flexible mounting, said recess being locatableadjacent the skull of the implantee in use thereby ensuring the magnetis held in the recess between the receiver component and the skull ofthe implantee.

In a thirteenth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein the external transmitter unit has a magnetpositioned therein and the implantable receiver component has amagnetised insert positioned therein to allow transcutaneous alignmentof said external transmitter unit and said implantable receivercomponent; [0031] the magnetised insert of the implantable receivercomponent having a first end and a second end and increasing in widthaway from said first end towards said second end, the first end beingpositionable closer to the skin of the implantee in use to ensureself-centering of the magnet of the external transmitter unit with themagnetised insert of the receiver component.

In a fourteenth aspect, there is provided a cochlear implant systemcomprising an external transmitter unit positionable on the outside ofan implantee's head and an implantable receiver component positionablesubcutaneously, wherein said external transmitter unit and saidimplantable receiver component each comprise a magnet therein to holdthe external transmitter unit substantially in transcutaneous alignmentwith the implantable receiver component; the system being characterisedin that the implantable receiver component is detachably connectable toan implantable cochlea stimulator device

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, exemplary embodiments are now described withreference to the accompanying drawings, in which:

FIG. 1 is a pictorial representation of a cochlear implant system;

FIG. 2 a is a schematic view of a magnet and mounting of one example ofthe invention;

FIG. 2 b depicts another arrangement for mounting the magnet in thereceiver component;

FIG. 3 depicts a still further arrangement for mounting the magnet inthe receiver component;

FIGS. 3 a and 3 b depict a still further arrangement for mounting themagnet in the receiver component;

FIGS. 4, 4 a and 4 b depict arrangements for identifying the location ofthe magnet in the mounting of the receiver component;

FIGS. 5 a and 5 b depict an alternative arrangement for mounting themagnet in the receiver component;

FIGS. 6 a and 6 b depict another arrangement for ensuring magneticalignment of the receiver component with the external transmittercomponent;

FIG. 7 a depicts a further arrangement for mounting the magnet in thereceiver component;

FIG. 7 b depicts how the magnet can be removed from the receivercomponent shown in FIG. 7 a;

FIGS. 8 a and 8 b depict an arrangement in which the receiver coil canbe disconnected from the stimulator component; and

FIGS. 9 a, 9 b, 9 c, 10 a, and 10 b depict various arrangements forretaining the magnet in the receiver component using one or moremanipulable clips.

DETAILED DESCRIPTION

Exemplary embodiments of a magnetic alignment system according to thepresent invention are generally depicted in the accompanying drawings aspart of a cochlear implant system.

As depicted pictorially in FIG. 1, the magnetic alignment system 10 of acochlear implant system comprises an external transmitter unit 11 and animplantable receiver component 12.

The external transmitter unit 11 comprises a transmitter antenna coil 13which transmits coded signals to the implantable receiver component 12via a radio frequency (RF) link.

The implantable receiver component 12 of the system comprises a receiverantenna coil 14 for receiving power and data from the transmitter coil13 and a stimulator unit 15 within a housing 16. A cable 17 extends fromthe stimulator unit 15 to the cochlea and terminates in an electrodearray 18. The signals received are applied by the array 18 to thebasilar membrane 19 thereby stimulating the auditory nerve 20.

The receiver coil 14 typically comprises a wire antenna coil comprisedof at least one and preferably two turns of electrically insulatedplatinum or gold wire.

The implantable receiver component 12 has a magnet to allowtranscutaneous alignment of the external transmitter unit 11 (which alsohas a magnet 9) and the implantable receiver component 12.

The electrical insulation of the antenna coil is provided by a flexiblesilicone molding. In use, the implantable receiver component 12 can bepositioned in a recess of the temporal bone adjacent the ear of animplantee.

Arrangements for preventing any or at least reducing substantialmovement of the magnet of a transcutaneous transmitter/receiver system,such as a cochlear implant system, while a recipient is undergoing MRIscans of relatively low field strengths and arrangements that allowremoval of the magnet from within the implantee if necessary, (such aswhen the recipient is to undergo MRI scans of relatively high fieldstrengths) are depicted in the remaining drawings.

In the embodiment depicted in FIG. 2 a, the implantable receivercomponent of a cochlear implant system has a magnet 21 and a mounting22. An outer surface of the magnet 21 has an engagement surface that isengageable with a complementary engagement surface formed in themounting 22. The engagement between the magnet 21 and the mounting 22minimises movement of the magnet, particularly when a patient undergoesan MRI procedure. Examples of the engagement surface and thecomplementary engagement surface are described in more detail below.

In FIG. 2 a, the magnet 21 has two extension members 23 that extend fromopposite sides of the magnet. The magnet 21 may be received by themounting 22 which is shown in FIG. 2 as a ring 24.

The ring 24 has at least one recessed portion 25. In an exemplaryembodiment, the ring 24 includes two recessed portions 25 although inFIG. 2 a, the second recessed portion is obscured from view. Therecessed portions 25 receive the extension members 23 of the magnet 21and hold the magnet in place within the ring 24.

The ring further includes two slots 26 in an inner surface 27 of thering 24. The slots 26 extend from an upper surface 28 of the ring 24 toa lower surface 29 of the ring 24, i.e. through the thickness of thering 24.

The magnet 21 may be relatively lowered into the center of the ring 24such that the extension members 23 pass through slots 26. When movedbeyond the lower surface 29 of the ring 24, the magnet is then rotatablymoveable relative to the ring 24.

The magnet 21 may be rotated until the extension members align with therecessed portions 25.

The ring 24 may sit on, or at least partially within, a resilientsilicone body of the implantable receiver component. To insert themagnet 21 into the center of the ring, a degree of force is thereforerequired to cause the extension member 23 to pass through the slots 26and beyond the lower surface 29 of the ring 24. Once the magnet 21 isrotated and the extension members 23 are in alignment with the recessedportions 25, release of any force applied to the magnet 21 will resultin the silicone body causing the extension members 23 to move up andaway from the lower surface 29 of the ring and into the recessedportions 25. With the extension members 23 housed within the recessedportions 25, the magnet 21 is no longer rotatably moveable relative tothe ring 24 (unless a degree of downward force is again applied to themagnet 21 to dislodge the extension members from the recessed portions).

The magnet 21 is, therefore, substantially but removably locked in placewithin the mounting 22.

Referring now to FIG. 2 b, an alternative arrangement is shown in whichthe extension members 23 a extend inwardly from the ring 24, and arearranged to engage with corresponding recessed portions 25 a provided onthe magnet 21. The number of slots 26 a is shown as two, however, it isenvisaged that one larger extension member 23 a on the ring 24 could beused together with a corresponding single slot on the magnet 21.

Further, the ring 24 as shown in FIG. 2 a has a series of holes 30extending therethrough. The silicone of the implantable receivercomponent may extend through the holes 30 and provides a means ofsecuring the ring 24 to the silicone body of the implantable receivercomponent. In this regard, portions of silicone may extend through theholes 30 and essentially act as rivets to mechanically lock the ring 24in place. This added level of security may be desirable when the magnetis subjected to MRI and particularly to high field strengths.

In this aspect, the engagement surface of the magnet or the magnetcasing can be a screw thread. The complementary engagement surface ofthe mounting can also be a screw thread that is formed in the mounting.In one embodiment, the mounting has a ring member mounted therein. Theinternal surface of the ring member may form the complementaryengagement surface and may be a screw thread. The ring member can bemade of a ceramic or plastics material. The mounting can be formed froma suitable biocompatible silicone.

As depicted in FIG. 3, the magnet can be screwed into or unscrewed fromthe mounting.

In FIG. 3, the outer surface of magnet 61 has a screw thread 62 formedtherein. The screw thread 62 is engageable with a complementary thread63 formed in a mounting ring 64 within the implantable component body(here depicted as 65). The mounting ring 64 can be made of a metal,ceramic or plastics material while the body 65 can be formed from asuitable biocompatible material, such as silicone.

As depicted, a top surface of the magnet 61 can have a slot 66 formedtherein that can receive a tool, such as an allen key 66 a as shown, ora screwdriver or the like, to facilitate turning of the magnet and itsremoval from the mounting ring 64.

In another embodiment, the engagement surface of the magnet may be heldin place within the mounting by friction fit. As described in moredetail below, the outer surface of the magnet, or casing of the magnet,can be shaped in a specific configuration, allowing for insertion of themagnet or part of the magnet into the mounting element. In this regard,the complementary engagement surface of the mounting will be compatiblewith the shape of the outer surface of the magnet or magnet casing suchthat the outer surface can be inserted into the mounting element. Oncethe outer surface of the magnet or magnet casing has been at leastpartially inserted into the mounting element, the magnet or magnetcasing may be rotated, for example a ¼ or ½ turn, thereby causing theshape of the engagement surface of the magnet or magnet casing to nolonger be compatible with the shape of the complementary engagementsurface of the mounting element. This thereby provides an interferencefit preventing inadvertent removal of the magnet from the mountingelement. In this embodiment, the magnet may be easily removed by merelyrotating the magnet the appropriate amount such that the shape of theengagement surface of the magnet means is compatible with the shape ofthe complementary engagement surface of the mounting element, therebyallowing easy removal of the magnet.

This particular embodiment is depicted in FIG. 3 a wherein magnet 61 isprovided with a pedestal element 61 a for securing within the mountingelement 64. In the depicted embodiment, the mounting element 64, issubstantially trapezoidal in shape with two upright walls 64 a, beingcurved in configuration. The pedestal element 61 a of the magnet 61 hasa similar shape to that of the mounting element 64, namely it has ashape consisting of two substantially parallel sides joined at both endsby curved portions. The pedestal is remote from the bottom face of themagnet 61, thereby forming a space between the pedestal element 61 a andthe magnet 61. The inner surfaces of the upright walls 64 a of themounting element 64 can be provided with a recess to receive the curvedend portions of the pedestal element 61 a when the pedestal is placedwithin the mounting element 64 for engagement.

In this regard, the magnet 61 is rotatable relative to the mounting. Themagnet may be rotated 90 degrees to the position shown in FIG. 3 a forlocating within the mounting element 64. Once the magnet 61 is placed inposition with the pedestal element 61 a located between the walls 64 aof the mounting element 64, the magnet is then rotated 90 degrees suchthat the curved walls of the pedestal element 61 a are received withinthe recessed curved walls of the mounting element 64. In this regard,the magnet is secured in place and is fixed within the mounting element64 as shown in FIG. 3 b. To remove the magnet 61 from the mountingelement 64 in the event, for example, of an MRI procedure, the magnet 61is rotated such that the pedestal element 61 a is no longer held inplace within the walls 64 a of the mounting element. The magnet can thenbe relatively easily removed. A screwdriver or other such tool can beused to assist in this procedure, via the slot 66.

As is shown in FIGS. 3 a and 3 b as the dotted line and the hashed arearespectively, the magnet 61 and mounting element 64 are preferablysecured in a flexible biocompatible material such as silicone. In thisregard, the silicone can be arranged so as to overlap the walls of themounting element 64 such that when the magnet 61 is placed in positionfor securing, as described above, the surrounding material may becompressed between the magnet 61 and the mounting element 64. In thisregard, the compression force may aid in securing the magnet in placewhen rotated into the secured position. Further, such an arrangement mayfurther seal the arrangement form the ingress of body fluids into themounting element 64.

In another embodiment, a spring-type force can be provided to aid in theinterference fit by providing a bias force between the engagementsurfaces of the magnet and the mounting element, such that when the twosurfaces are in non-alignment, the magnet will be securely held inplace. Such a biasing force can be provided by placing a spring means orspring member in the mounting for receiving the magnet, or by providinga compressive material such as silicone within the mounting, that iscompressed once the magnet is inserted into the mounting and provides aforce that biases the magnet against the mounting.

A further aspect of the invention is depicted in FIGS. 4, 4 a and 4 b.The magnet (here depicted as 51) of the implantable receiver componentis housed within a suitable biocompatible flexible silicone mounting 52.In FIG. 4, the mounting 52 has a circular indentation 53 formed thereinthat acts as an indicia and serves to assist in identifying the locationof the magnet 51 within the mounting 52. During surgery to remove themagnet 51, the ring 53 will indicate to the surgeon the location of themagnet 51 within the mounting 52. The indentation can also serve as aguide to a scalpel blade used to cut through the mounting 52 to accessthe magnet 51.

In the embodiment depicted in FIGS. 4 a and 4 b, the indicia cancomprise two or more holes 54 formed in the silicone. The holes 54 againact as guides to a surgeon having to cut the magnet 51 from the mounting52. That is, they identify where the mounting 52 should be cut to allowremoval of the magnet 51 held therein.

FIGS. 5 a and 5 b depict a still further arrangement wherein the magnet71 of the implantable receiver component is housed within a pocket 72formed in a wall of the biocompatible flexible mounting. The pocket 72has a restricted opening 73 formed therein through which the magnet 71can be inserted but which is sized to retain the magnet 71 within thepocket 72 following insertion during normal use.

FIGS. 6 a and 6 b depict a still further arrangement, in which theexternal transmitter unit (not depicted in FIGS. 6 a and 6 b) has amagnet positioned therein while the implantable receiver component (heredepicted as 80) has a conical, non-magnetised ferro-magnetic insert 81positioned therein to allow transcutaneous alignment of the externaltransmitter unit and the implantable receiver component. Thenon-magnetised insert 81 of the implantable receiver component has afirst end and a second end and increases in width away from the firstend towards the second end, the first end being adapted to be positionedcloser to the skin of the implantee to ensure self-centering of themagnet of the external transmitter unit with the insert 81 of thereceiver component. While depicted as a conical structure, themagnetised insert be other shapes such as a frusto-conical shape.

The non-magnetised insert 81 can be mounted in a non-magnetic supportwithin the receiver component. In one embodiment, the support can be atitanium case 82 as depicted in FIG. 6 b. In another embodiment, asdepicted in FIG. 6 a, a suitable non-magnetic material, such as plastic,ceramic or titanium, stop member 83 can lock the insert 81 in thereceiver component.

While the insert 81 can be removable, the use of a non-magnetised insert81 rather than a magnet has the advantage of reducing the magnetic forceon the receiver component during an MRI scan if it is left in place.

In FIGS. 7 a and 7 b, the magnet 91 of the implantable receivercomponent (here depicted as 92) is housed within a recess 93 formed in asuitable biocompatible flexible mounting. The recess 93 is adapted to belocated adjacent the skull 94 of the implantee in use thereby ensuringthe magnet 91 is held in the recess 93 between the receiver component 92and the skull 94 of the implantee.

In this embodiment, the magnet 91 can be removed from the recess byincising the skin of the implantee and then gently lifting the receivercomponent 92 away from the skull a distance sufficient to allow asurgeon to reach under the receiver component and remove the magnet 91from the recess 93, as is depicted in FIG. 7 b.

FIGS. 8 a and 8 b depict a further arrangement in which the mounting 101housing the receiver coil 102 and magnet 103 is detachably connectableto an implantable tissue stimulator device (here depicted as 104).Electrical connection is made between the receiver component and thetissue stimulator device when the component is connected to thestimulator device. A pin and socket arrangement can be used to providethe electrical connection.

As depicted, the electrical connection is made between the coil 102 andthe circuitry of the tissue stimulator device 104 by a pin and socketarrangement 105. Once connection is made, the pin and socket arrangementis preferably constructed such that there is no ingress of bodily fluidsinto either the stimulator device 104 or the mounting 101. In oneembodiment, the socket can be mounted to the stimulator device and thepin or pins to the receiver component. An arrangement where the socketis part of the receiver component and the pin or pins are part of thestimulator device can be equally envisaged.

If the implantee is to undergo an MRI scan, an incision can be made inthe implantee, and the receiver component detached from the tissuestimulator device. The entire receiver component, as defined in thisaspect, is then removed rather than just the magnet. Once the MRI scanis complete, the receiver component can be re-implanted and thenecessary connection again made between the receiver component and thestimulator device.

Mounting 101 is detachable from the tissue stimulator device 104 and maybe removed prior to an MRI procedure. Once the MRI scan is complete, themounting 101 can be re-implanted and the necessary connection again madebetween the coil 102 and the stimulator device 104.

In FIGS. 9 a, 9 b, 9 c, 10 a and 10 b various systems that rely on oneor more clips to removably hold the magnet within the receiver componentare depicted.

The clips can be mounted on the receiver component and adapted to engagethe magnet positioned therein or thereon. In another embodiment, theclips can be mounted to the magnet or a casing thereof and areengageable with the receiver component. The clips may be manipulable bya surgeon.

FIG. 9 a depicts a compression clip 111 that can be used to compress asilicone pocket 112 around a magnet (here depicted as 113). The clip 111can be removed by a surgeon if removal of the magnet 113 is required.

In the embodiment depicted in FIGS. 9 b and 9 c, two clips 114 aremounted on the magnet 113 and are engageable with a socket member 115that is itself removably engageable in the receiver component (heredepicted as 116). The socket member 115 has a main member 120 and twowing members 117. The wing members 117 are engageable within recesses118 extending laterally from a main recess 119 formed in the receivercomponent 116. When the socket member 115 is positioned within the mainrecess 119 and the wing members 117 are engaged with the lateralrecesses 118, the main member 120 is suspended across the main recess119.

The clips 114 of the magnet 113 are preferentially biased inwardly andas such must be moved out and around the main member 120 on insertion.Once the lower ends of the clips 114 have moved relatively below themain member 120, the clips 114 can be released and so engage under themain member 120. If it is desired to remove the magnet 113, the clips114 are pulled relatively apart by the surgeon thereby allowing themagnet 113 to be drawn up and out of the main recess 119.

An alternative arrangement for using a clip to retain the magnet 113 inthe receiver component 116 is depicted in FIGS. 10 a and 10 b. In thisembodiment, a clip 121 is positioned underneath the magnet 113. The clip121 is supported in the silicone body of the receiver component and hastwo lips 122 that preferentially hold the magnet 113 in place duringnormal use. If it is desired to remove the magnet 113, the lips 122 arepushed down into the resilient silicone body 116 and pivot aboutuprights 123 so allowing the magnet 113 to be popped out of the receivercomponent 116 in the direction of arrow A.

The cochlear implant system described above enables an implantee toundergo an MRI procedure without removing the magnet of an implant, suchas a cochlear implant, or provides a system enabling easy removal of themagnet to facilitate an MRI procedure at relatively higher filedstrengths. Such a system is particularly useful for those implanteesrequiring regular MRI scans.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. A medical device comprising: an implantablecomponent including: a magnet; and a structural component secured in theimplantable component and configured to restrain movement of the magnetrelative to the implantable component in at least a first directionparallel to a first axis of a Cartesian coordinate system.
 2. Themedical device of claim 1, wherein: the magnet is restrained frommovement in the first direction via a bias force between the structuralcomponent and the magnet.
 3. The medical device of claim 1, wherein: theimplantable component is configured such that the magnet is removablefrom the implantable component through the bottom of the implantablecomponent.
 4. The medical device of claim 1, wherein: the implantablecomponent configured to permit the magnet to rotate relative to thestructural component.
 5. The medical device of claim 1, wherein: thestructural component is configured to permit the magnet to rotaterelative to the structural component about a second axis of theCartesian coordinate system, wherein the first axis is normal to thesecond axis.
 6. The medical device of claim 1, wherein: the structuralcomponent is configured to permit the magnet to rotate relative to thestructural component about the first axis.
 7. The medical device ofclaim 1, wherein: the magnet is rotatably movable relative to thestructural component while restrained from movement in the firstdirection by the structural component.
 8. A medical device comprising:an implantable component including: a magnet; and a chassis secured inthe component and configured to removably support the magnet while themagnet is located within the implantable component, wherein theimplantable component includes a silicone body, and the silicone body atleast partially envelopes the chassis and the magnet while the magnet islocated in the chassis.
 9. The medical device of claim 8, wherein: thesilicone body complete envelops the magnet.
 10. The medical device ofclaim 8, wherein: the implantable component is configured such that,while the implantable component is implanted in a recipient, thesilicone body is at least partially separable so as to create a paththrough the silicone body through which the magnet can be removedtherethrough to remove the magnet from the implantable component. 11.The medical device of claim 8, wherein: the chassis is in the form of adoughnut around the magnet; and the chassis is made of ceramic.
 12. Themedical device of claim 8, wherein: the implantable component isconfigured such that the magnet is removable from the implantablecomponent through the bottom of the implantable component.
 13. Themedical device of claim 8, wherein: the magnet is disk shaped, and themagnet is rotatable relative to the chassis about a longitudinaldirection of the magnet.
 14. The medical device of claim 8, wherein: themagnet is disk shaped, and the magnet is rotatable relative to thechassis about a longitudinal direction of the magnet and prevented fromrotating relative to the chassis about an axis normal to thelongitudinal direction.
 15. A method of reducing deleterious effects ofan MRI scan on a recipient having an implanted medical device whichincludes a magnet, comprising: obtaining access to a recipient in whichthe implanted medical device is implanted; rotating the magnet while themagnet is implanted in the recipient relative to a main body of theimplanted medical device; and subjecting the recipient to an MRI scan.16. The method of claim 51, further comprising: prior to rotating themagnet, cutting into the skin of the recipient to access the implantedmedical device.
 17. The method of claim 15, further comprising:subsequent to the action of rotating the magnet, removing the magnetfrom the recipient.
 18. The method of claim 15, wherein: the action ofobtaining access to the recipient is executed prior to the action ofrotating the magnet and the action of rotating the magnet is executedprior to subjecting the recipient to the MRI scan.
 19. The method ofclaim 15, wherein: the magnet is part of a magnet assembly, wherein themagnet assembly includes a casing for the magnet; and the medical deviceincludes a chassis surrounding the magnet assembly.
 20. The method ofclaim 15, wherein: the implantable component includes a structuralcomponent that extends completely about the magnet, which structuralcomponent is connected to a silicone body that is in contact with boneof the recipient, wherein the rotation of the magnet entails rotation ofthe magnet relative to the structural component.
 21. The method of claim15, further comprising: subsequent to the action of rotating the magnet,removing the magnet from the recipient through the bottom of theimplanted medical device.